Sensing frame averaging for cancelling display noise in simultaneous display and touch sensing

ABSTRACT

Techniques for removing display-based corrupting components from a capacitive sensing signal when display and capacitive sensing is performed at or nearly at the same time. A routing carrying display related signals (e.g., a source signal for sub-pixel updating) may induce a corrupting current into a routing for carrying capacitive sensing signals. This corrupting current would reduce the ability to determine presence of an input object via the sensing signal. Therefore, the corrupting signal is effectively removed by averaging sensing signals from two consecutive frames together. Because displays perform frame inversion, in which the voltage polarity provided to a sub-pixel for updates is reversed each frame, the corrupting current reverses in polarity each frame. Therefore, adding two subsequent frames together cancels out the corrupting signal.

BACKGROUND

Field of the Disclosure

Embodiments generally relate to input sensing and, in particular, tocancelling display noise in simultaneous display and touch sensing.

Description of the Related Art

Input devices including proximity sensor devices (also commonly calledtouchpads or touch sensor devices) are widely used in a variety ofelectronic systems. A proximity sensor device typically includes asensing region, often demarked by a surface, in which the proximitysensor device determines the presence, location, and/or motion of one ormore input objects. Proximity sensor devices may be used to provideinterfaces for the electronic system. For example, proximity sensordevices are often used as input devices for larger computing systems(such as opaque touchpads integrated in, or peripheral to, notebook ordesktop computers). Proximity sensor devices are also often used insmaller computing systems (such as touch screens integrated in cellularphones).

Proximity sensor devices may include display elements that are drivenfor updates simultaneously with performing proximity sensing. A routingcarrying display related signals (e.g., a source signal for sub-pixelupdating) to the display elements may induce a corrupting current into arouting for carrying proximity sensing signal. This corrupting currentwould reduce the ability to determine presence of an input object viathe sensing signal.

SUMMARY

A processing system configured for simultaneously updating a display andperforming capacitive sensing is provided. The processing systemincludes a source driver configured to drive a source line with a firstsource driver voltage during a first time period and to receiveresulting signals on a routing trace coupled to a sensor electrodeduring a second time period that at least partially overlaps with thefirst time period, the routing trace and the source line being routedproximate each other. The processing system also includes aninterference remover configured to acquire first resulting signalsduring a first display update period and second resulting signals duringa second display update period, and to remove display interference fromthe second resulting signals by combining the first resulting signalsand the second resulting signals. First display signals provided fordisplay updates during the first display update period areframe-inverted with respect to second display signals provided fordisplay updates during the second display update period.

An input device configured for simultaneously updating a display andperforming capacitive sensing is provided. The input device includes adisplay element coupled to a source line. The input device also includesa sensor electrode coupled to a routing trace, the routing trace and thesource line being routed proximate each other. The input device furtherincludes a processing system coupled to the source line and the routingtrace. The processing system includes a source driver configured todrive a source line with a first source driver voltage during a firsttime period and to receive resulting signals on a routing trace coupledto a sensor electrode during a second time period that at leastpartially overlaps with the first time period, the routing trace and thesource line being routed proximate each other. The processing systemalso includes an interference remover configured to acquire firstresulting signals during a first display update period and secondresulting signals during a second display update period, and to removedisplay interference from the second resulting signals by combining thefirst resulting signals and the second resulting signals. First displaysignals provided for display updates during the first display updateperiod are frame-inverted with respect to second display signalsprovided for display updates during the second display update period.

A method for simultaneously updating a display and performing capacitivesensing is provided. The method includes driving a source line with afirst source driver voltage during a first time period. The method alsoincludes receiving resulting signals on a routing trace coupled to asensor electrode during a second time period that at least partiallyoverlaps with the first time period, the routing trace and the sourceline being routed proximate each other. The method further includesacquiring first resulting signals during a first display update periodand second resulting signals during a second display update period. Themethod also includes removing display interference from the secondresulting signals by combining the first resulting signals and thesecond resulting signals. First display signals provided for displayupdates during the first display update period are frame-inverted withrespect to second display signals provided for display updates duringthe second display update period.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of embodimentscan be understood in detail, a more particular description ofembodiments, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments and are therefore not to be considered limiting ofscope, for other effective embodiments may be admitted.

FIG. 1 is a block diagram of a system that includes an input deviceaccording to an example.

FIG. 2A is a block diagram depicting a capacitive sensor deviceaccording to an example.

FIG. 2B is a block diagram depicting another capacitive sensor deviceaccording to an example.

FIG. 3 is a schematic diagram of a routing configuration, according toan example.

FIG. 4 is a diagram that illustrates aspects of frame inversion,according to an example.

FIG. 5 is a graph that illustrates the effect of frame inversion for aparticular sub-pixel, according to an example.

FIG. 6 is a graph illustrating frame averaging for cancellation ofcorruption current, according to an example.

FIG. 7 is a flow diagram of a method for removing corruptingcontribution generated by display elements from a sensing signal,according to an example.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements of one embodiment may bebeneficially incorporated in other embodiments.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the embodiments or the application and uses ofsuch embodiments. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

Various embodiments provide techniques for removing display-basedcorrupting components from a capacitive sensing signal when display andcapacitive sensing is performed at or nearly at the same time. A routingcarrying display related signals (e.g., a source signal for sub-pixelupdating) may induce a corrupting current into a routing for carryingcapacitive sensing signals. This corrupting current would reduce theability to determine presence of an input object via the sensing signal.Therefore, the corrupting signal is effectively removed by averagingsensing signals from two consecutive frames together. Because displaysperform frame inversion, in which the voltage polarity provided to asub-pixel for updates is reversed each frame, the corrupting currentreverses in polarity each frame. Therefore, adding two subsequent framestogether cancels out the corrupting signal.

Turning now to the figures, FIG. 1 is a block diagram of an exemplaryinput device 100 in accordance with embodiments of the invention. Theinput device 100 may be configured to provide input to an electronicsystem (not shown). As used in this document, the term “electronicsystem” (or “electronic device”) broadly refers to any system capable ofelectronically processing information. Some non-limiting examples ofelectronic systems include personal computers of all sizes and shapes,such as desktop computers, laptop computers, netbook computers, tablets,web browsers, e-book readers, and personal digital assistants (PDAs).Additional example electronic systems include composite input devices,such as physical keyboards that include input device 100 and separatejoysticks or key switches. Further example electronic systems includeperipherals such as data input devices (including remote controls andmice), and data output devices (including display screens and printers).Other examples include remote terminals, kiosks, and video game machines(e.g., video game consoles, portable gaming devices, and the like).Other examples include communication devices (including cellular phones,such as smart phones), and media devices (including recorders, editors,and players such as televisions, set-top boxes, music players, digitalphoto frames, and digital cameras). Additionally, the electronic systemcould be a host or a slave to the input device.

The input device 100 can be implemented as a physical part of theelectronic system or can be physically separate from the electronicsystem. As appropriate, the input device 100 may communicate with partsof the electronic system using any one or more of the following: buses,networks, and other wired or wireless interconnections. Examples includeI²C, SPI, PS/2, Universal Serial Bus (USB), Bluetooth, RF, and IRDA.

In FIG. 1, the input device 100 is shown as a proximity sensor device(also often referred to as a “touchpad” or a “touch sensor device”)configured to sense input provided by one or more input objects 140 in asensing region 120. Example input objects include fingers and styli, asshown in FIG. 1.

Sensing region 120 encompasses any space above, around, in, and/or nearthe input device 100 in which the input device 100 is able to detectuser input (e.g., user input provided by one or more input objects 140).The sizes, shapes, and locations of particular sensing regions may varywidely from embodiment to embodiment. In some embodiments, the sensingregion 120 extends from a surface of the input device 100 in one or moredirections into space until signal-to-noise ratios prevent sufficientlyaccurate object detection. The distance to which this sensing region 120extends in a particular direction, in various embodiments, may be on theorder of less than a millimeter, millimeters, centimeters, or more, andmay vary significantly with the type of sensing technology used and theaccuracy desired. Thus, some embodiments sense input that comprises nocontact with any surfaces of the input device 100 contact with an inputsurface (e.g., a touch surface) of the input device 100 contact with aninput surface of the input device 100 coupled with some amount ofapplied force or pressure, and/or a combination thereof. In variousembodiments, input surfaces may be provided by surfaces of casingswithin which the sensor electrodes reside, by face sheets applied overthe sensor electrodes or any casings, etc. In some embodiments, thesensing region 120 has a rectangular shape when projected onto an inputsurface of the input device 100.

The input device 100 may utilize any combination of sensor componentsand sensing technologies to detect user input in the sensing region 120.The input device 100 comprises one or more sensing elements fordetecting user input. As several non-limiting examples, the input device100 may use capacitive, elastive, resistive, inductive, magnetic,acoustic, ultrasonic, and/or optical techniques. Some implementationsare configured to provide images that span one, two, three, or higherdimensional spaces. Some implementations are configured to provideprojections of input along particular axes or planes. In some resistiveimplementations of the input device 100 a flexible and conductive firstlayer is separated by one or more spacer elements from a conductivesecond layer. During operation, one or more voltage gradients arecreated across the layers. Pressing the flexible first layer may deflectit sufficiently to create electrical contact between the layers,resulting in voltage outputs reflective of the point(s) of contactbetween the layers. These voltage outputs may be used to determinepositional information.

In some inductive implementations of the input device 100 one or moresensing elements pick up loop currents induced by a resonating coil orpair of coils. Some combination of the magnitude, phase, and frequencyof the currents may then be used to determine positional information.

In some capacitive implementations of the input device 100, voltage orcurrent is applied to create an electric field. Nearby input objectscause changes in the electric field and produce detectable changes incapacitive coupling that may be detected as changes in voltage, current,or the like.

Some capacitive implementations utilize arrays or other regular orirregular patterns of capacitive sensing elements to create electricfields. In some capacitive implementations, separate sensing elementsmay be ohmically shorted together to form larger sensor electrodes. Somecapacitive implementations utilize resistive sheets, which may beuniformly resistive.

Some capacitive implementations utilize “self capacitance” (or “absolutecapacitance”) sensing methods based on changes in the capacitivecoupling between sensor electrodes and an input object. In variousembodiments, an input object near the sensor electrodes alters theelectric field near the sensor electrodes, changing the measuredcapacitive coupling. In one implementation, an absolute capacitancesensing method operates by modulating sensor electrodes with respect toa reference voltage (e.g., system ground) and by detecting thecapacitive coupling between the sensor electrodes and input objects.

Some capacitive implementations utilize “mutual capacitance” (or“transcapacitance”) sensing methods based on changes in the capacitivecoupling between sensor electrodes. In various embodiments, an inputobject near the sensor electrodes alters the electric field between thesensor electrodes, changing the measured capacitive coupling. In oneimplementation, a transcapacitive sensing method operates by detectingthe capacitive coupling between one or more transmitter sensorelectrodes (also “transmitter electrodes” or “transmitters”) and one ormore receiver sensor electrodes (also “receiver electrodes” or“receivers”). Transmitter sensor electrodes may be modulated relative toa reference voltage (e.g., system ground) to transmit transmittersignals. Receiver sensor electrodes may be held substantially constantrelative to the reference voltage to facilitate receipt of resultingsignals. A resulting signal may comprise effect(s) corresponding to oneor more transmitter signals and/or to one or more sources ofenvironmental interference (e.g., other electromagnetic signals). Sensorelectrodes may be dedicated transmitters or receivers, or sensorelectrodes may be configured to both transmit and receive.Alternatively, the receiver electrodes may be modulated relative toground.

In FIG. 1, a processing system 110 is shown as part of the input device100. The processing system 110 is configured to operate the hardware ofthe input device 100 to detect input in the sensing region 120. Theprocessing system 110 comprises parts of, or all of, one or moreintegrated circuits (ICs) and/or other circuitry components. Forexample, a processing system for a mutual capacitance sensor device maycomprise transmitter circuitry configured to transmit signals withtransmitter sensor electrodes and/or receiver circuitry configured toreceive signals with receiver sensor electrodes. In some embodiments,the processing system 110 also comprises electronically-readableinstructions, such as firmware code, software code, and/or the like. Insome embodiments, components composing the processing system 110 arelocated together, such as near sensing element(s) of the input device100. In other embodiments, components of processing system 110 arephysically separate with one or more components close to sensingelement(s) of input device 100 and one or more components elsewhere. Forexample, the input device 100 may be a peripheral coupled to a desktopcomputer, and the processing system 110 may comprise software configuredto run on a central processing unit of the desktop computer and one ormore ICs (perhaps with associated firmware) separate from the centralprocessing unit. As another example, the input device 100 may bephysically integrated in a phone, and the processing system 110 maycomprise circuits and firmware that are part of a main processor of thephone. In some embodiments, the processing system 110 is dedicated toimplementing the input device 100. In other embodiments, the processingsystem 110 also performs other functions, such as operating displayscreens, driving haptic actuators, etc.

The processing system 110 may be implemented as a set of modules thathandle different functions of the processing system 110. Each module maycomprise circuitry that is a part of the processing system 110,firmware, software, or a combination thereof. In various embodiments,different combinations of modules may be used. Example modules includehardware operation modules for operating hardware such as sensorelectrodes and display screens, data processing modules for processingdata such as sensor signals and positional information, and reportingmodules for reporting information. Further example modules includesensor operation modules configured to operate sensing element(s) todetect input, identification modules configured to identify gesturessuch as mode changing gestures, and mode changing modules for changingoperation modes.

In some embodiments, the processing system 110 responds to user input(or lack of user input) in the sensing region 120 directly by causingone or more actions. Example actions include changing operation modes,as well as GUI actions such as cursor movement, selection, menunavigation, and other functions. In some embodiments, the processingsystem 110 provides information about the input (or lack of input) tosome part of the electronic system (e.g., to a central processing systemof the electronic system that is separate from the processing system110, if such a separate central processing system exists). In someembodiments, some part of the electronic system processes informationreceived from the processing system 110 to act on user input, such as tofacilitate a full range of actions, including mode changing actions andGUI actions.

For example, in some embodiments, the processing system 110 operates thesensing element(s) of the input device 100 to produce electrical signalsindicative of input (or lack of input) in the sensing region 120. Theprocessing system 110 may perform any appropriate amount of processingon the electrical signals in producing the information provided to theelectronic system. For example, the processing system 110 may digitizeanalog electrical signals obtained from the sensor electrodes. Asanother example, the processing system 110 may perform filtering orother signal conditioning. As yet another example, the processing system110 may subtract or otherwise account for a baseline, such that theinformation reflects a difference between the electrical signals and thebaseline. As yet further examples, the processing system 110 maydetermine positional information, recognize inputs as commands,recognize handwriting, and the like.

“Positional information” as used herein broadly encompasses absoluteposition, relative position, velocity, acceleration, and other types ofspatial information. Exemplary “zero-dimensional” positional informationincludes near/far or contact/no contact information. Exemplary“one-dimensional” positional information includes positions along anaxis. Exemplary “two-dimensional” positional information includesmotions in a plane. Exemplary “three-dimensional” positional informationincludes instantaneous or average velocities in space. Further examplesinclude other representations of spatial information. Historical dataregarding one or more types of positional information may also bedetermined and/or stored, including, for example, historical data thattracks position, motion, or instantaneous velocity over time.

In some embodiments, the input device 100 is implemented with additionalinput components that are operated by the processing system 110 or bysome other processing system. These additional input components mayprovide redundant functionality for input in the sensing region 120 orsome other functionality. FIG. 1 shows buttons 130 near the sensingregion 120 that can be used to facilitate selection of items using theinput device 100. Other types of additional input components includesliders, balls, wheels, switches, and the like. Conversely, in someembodiments, the input device 100 may be implemented with no other inputcomponents.

In some embodiments, the input device 100 comprises a touch screeninterface, and the sensing region 120 overlaps at least part of anactive area of a display screen. For example, the input device 100 maycomprise substantially transparent sensor electrodes overlaying thedisplay screen and provide a touch screen interface for the associatedelectronic system. The display screen may be any type of dynamic displaycapable of displaying a visual interface to a user, and may include anytype of light emitting diode (LED), organic LED (OLED), cathode ray tube(CRT), liquid crystal display (LCD), plasma, electroluminescence (EL),or other display technology. The input device 100 and the display screenmay share physical elements. For example, some embodiments may utilizesome of the same electrical components for displaying and sensing. Asanother example, the display screen may be operated in part or in totalby the processing system 110.

It should be understood that while many embodiments of the invention aredescribed in the context of a fully functioning apparatus, themechanisms of the present invention are capable of being distributed asa program product (e.g., software) in a variety of forms. For example,the mechanisms of the present invention may be implemented anddistributed as a software program on information bearing media that arereadable by electronic processors (e.g., non-transitorycomputer-readable and/or recordable/writable information bearing mediareadable by the processing system 110). Additionally, the embodiments ofthe present invention apply equally regardless of the particular type ofmedium used to carry out the distribution. Examples of non-transitory,electronically readable media include various discs, memory sticks,memory cards, memory modules, and the like. Electronically readablemedia may be based on flash, optical, magnetic, holographic, or anyother storage technology.

FIG. 2A is a block diagram depicting a capacitive sensor device 200Aaccording to an example. The capacitive sensor device 200A comprises anexample implementation of the input device 100 shown in FIG. 1. Thecapacitive sensor device 200A includes a sensor electrode collection 208coupled to an example implementation of the processing system 110(referred to as “the processing system 110A”). As used herein, generalreference to the processing system 110 is a reference to the processingsystem described in FIG. 1 or any other embodiment thereof describedherein (e.g., the processing system 110A, 110B, etc.).

The sensor electrode collection 208 is disposed on a substrate 202 toprovide the sensing region 120. The sensor electrode collection 208includes sensor electrodes disposed on the substrate 202. In the presentexample, the sensor electrode collection 208 includes two pluralities ofsensor electrodes 220-1 through 220-N (collectively “sensor electrodes220”), and 230 -1 through 230-M (collectively “sensor electrodes 230”),where M and N are integers greater than zero. The sensor electrodes 220and 230 are separated by a dielectric (not shown). The sensor electrodes220 and the sensor electrodes 230 can be non-parallel. In an example,the sensor electrodes 220 are disposed orthogonally with the sensorelectrodes 230.

In some examples, the sensor electrodes 220 and the sensor electrodes230 can be disposed on separate layers of the substrate 202. In otherexamples, the sensor electrodes 220 and the sensor electrodes 230 can bedisposed on a single layer of the substrate 202. While the sensorelectrodes are shown disposed on a single substrate 202, in someembodiments, the sensor electrodes can be disposed on more than onesubstrate. For example, some sensor electrodes can be disposed on afirst substrate, and other sensor electrodes can be disposed on a secondsubstrate adhered to the first substrate.

In the present example, the sensor electrode collection 208 is shownwith the sensor electrodes 220, 230 generally arranged in a rectangulargrid of intersections of orthogonal sensor electrodes. It is to beunderstood that the sensor electrode collection 208 is not limited tosuch an arrangement, but instead can include numerous sensor patterns.Although the sensor electrode collection 208 is depicted as rectangular,the sensor electrode collection 208 can have other shapes, such as acircular shape.

As discussed below, the processing system 110A can operate the sensorelectrodes 220, 230 according to a plurality of excitation schemes,including excitation scheme(s) for mutual capacitance sensing(“transcapacitive sensing”) and/or self-capacitance sensing (“absolutecapacitive sensing”). In a transcapacitive excitation scheme, theprocessing system 110A drives the sensor electrodes 230 with transmittersignals (the sensor electrodes 230 are “transmitter electrodes”), andreceives resulting signals from the sensor electrodes 220 (the sensorelectrodes 220 are “receiver electrodes”). In some embodiments, sensorelectrodes 220 may be transmitter electrodes and sensor electrodes 230may be receiver electrodes. The sensor electrodes 230 can have the sameor different geometry as the sensor electrodes 220. In an example, thesensor electrodes 230 are wider and more closely distributed than thesensor electrodes 220, which are thinner and more sparsely distributed.Similarly, in an embodiment, sensor electrodes 220 may be wider and/ormore sparsely distributed. Alternatively, the sensor electrodes 220, 230can have the same width and/or the same distribution.

The sensor electrodes 220 and the sensor electrodes 230 are coupled tothe processing system 110A by conductive routing traces 204 andconductive routing traces 206, respectively. The processing system 110Ais coupled to the sensor electrodes 220, 230 through the conductiverouting traces 204, 206 to implement the sensing region 120 for sensinginputs. Each of the sensor electrodes 220 can be coupled to at least onerouting trace of the routing traces 206. Likewise, each of the sensorelectrodes 230 can be coupled to at least one routing trace of therouting traces 204.

FIG. 2B is a block diagram depicting a capacitive sensor device 200Baccording to an example. The capacitive sensor device 200B comprisesanother example implementation of the input device 100 shown in FIG. 1.In the present example, the sensor electrode collection 208 includes aplurality of sensor electrodes 210 _(1,1) through 210 _(J,K), where Jand K are integers (collectively “sensor electrodes 210”). The sensorelectrodes 210 are ohmically isolated from each other and the gridelectrode 214. The sensor electrodes 210 can be separated from the gridelectrode 214 by a gap 216. In the present example, the sensorelectrodes 210 are arranged in a rectangular matrix pattern, where atleast one of J or K is greater than zero. The sensor electrodes 210 canbe arranged in other patterns, such as polar arrays, repeating patterns,non-repeating patterns, or like type arrangements. In variousembodiments, the grid electrode(s) is optional and may not be included.Similar to the capacitive sensor device 200A, the processing system 110Acan operate the sensor electrodes 210 and the grid electrode 214according to a plurality of excitation schemes, including excitationscheme(s) for transcapacitive sensing and/or absolute capacitivesensing.

In some examples, the sensor electrodes 210 and the grid electrode 214can be disposed on separate layers of the substrate 202. In otherexamples, the sensor electrodes 210 and the grid electrode 214 can bedisposed on a single layer of the substrate 202. The sensor electrodes210 can be on the same and/or different layers as the sensor electrodes220 and the sensor electrodes 230. While the sensor electrodes are showndisposed on a single substrate 202, in some embodiments, the sensorelectrodes can be disposed on more than one substrate. For example, somesensor electrodes can be disposed on a first substrate, and other sensorelectrodes can be disposed on a second substrate adhered to the firstsubstrate.

The sensor electrodes 210 are coupled to the processing system 110A byconductive routing traces 212. The processing system 110A can also becoupled to the grid electrode 214 through one or more routing traces(not shown for clarity). The processing system 110A is coupled to thesensor electrodes 210 through the conductive routing traces 212 toimplement the sensing region 120 for sensing inputs.

Referring to FIGS. 2A and 2B, the capacitive sensor device 200A or 200Bcan be utilized to communicate user input (e.g., a user's finger, aprobe such as a stylus, and/or some other external input object) to anelectronic system (e.g., computing device or other electronic device).For example, the capacitive sensor device 200A or 200B can beimplemented as a capacitive touch screen device that can be placed overan underlying image or information display device (not shown). In thismanner, a user would view the underlying image or information display bylooking through substantially transparent elements in the sensorelectrode collection 208. When implemented in a touch screen, thesubstrate 202 can include at least one substantially transparent layer(not shown). The sensor electrodes and the conductive routing traces canbe formed of substantially transparent conductive material. Indium tinoxide (ITO) and/or thin, barely visible wires are but two of manypossible examples of substantially transparent material that can be usedto form the sensor electrodes and/or the conductive routing traces. Inother examples, the conductive routing traces can be formed ofnon-transparent material, and then hidden in a border region (not shown)of the sensor electrode collection 208.

In another example, the capacitive sensor device 200A or 200B can beimplemented as a capacitive touchpad, slider, button, or othercapacitance sensor. For example, the substrate 202 can be implementedwith, but not limited to, one or more clear or opaque materials.Likewise, clear or opaque conductive materials can be utilized to formsensor electrodes and/or conductive routing traces for the sensorelectrode collection 208.

In general, the processing system 110A excites or drives sensingelements of the sensor electrode collection 208 with a sensing signaland measures an induced or resulting signal that includes the sensingsignal and effects of input in the sensing region 120. The terms“excite” and “drive” as used herein encompasses controlling someelectrical aspect of the driven element. For example, it is possible todrive current through a wire, drive charge into a conductor, drive asubstantially constant or varying voltage waveform onto an electrode,etc. A sensing signal can be constant, substantially constant, orvarying over time, and generally includes a shape, frequency, amplitude,and phase. A sensing signal can be referred to as an “active signal” asopposed to a “passive signal,” such as a ground signal or otherreference signal. A sensing signal can also be referred to as a“transmitter signal” when used in transcapacitive sensing, or an“absolute sensing signal” or “modulated signal” when used in absolutesensing.

In an example, the processing system 110A drives sensing element(s) ofthe sensor electrode collection 208 with a voltage and senses resultingrespective charge on sensing element(s). That is, the sensing signal isa voltage signal and the resulting signal is a charge signal (e.g., asignal indicative of accumulated charge, such as an integrated currentsignal). Capacitance is proportional to applied voltage and inverselyproportional to accumulated charge. The processing system 110A candetermine measurement(s) of capacitance from the sensed charge. Inanother example, the processing system 110A drives sensing element(s) ofthe sensor electrode collection 208 with charge and senses resultingrespective voltage on sensing element(s). That is, the sensing signal isa signal to cause accumulation of charge (e.g., current signal) and theresulting signal is a voltage signal. The processing system 110A candetermine measurement(s) of capacitance from the sensed voltage. Ingeneral, the term “sensing signal” is meant to encompass both drivingvoltage to sense charge and driving charge to sense voltage, as well asany other type of signal that can be used to obtain indicia ofcapacitance. “Indicia of capacitance” include measurements of charge,current, voltage, and the like, from which capacitance can be derived.

The processing system 110A can include a sensor module 240 and adetermination module 260. The sensor module 240 and the determinationmodule 260 comprise modules that perform different functions of theprocessing system 110A. In other examples, different configurations ofone or more modules can perform the functions described herein. Thesensor module 240 and the determination module 260 can include circuitry275 and can also include firmware, software, or a combination thereofoperating in cooperation with the circuitry 275.

The sensor module 240 selectively drives sensing signal(s) on one ormore sensing elements of the sensor electrode collection 208 over one ormore cycles (“excitation cycles”) in accordance with one or more schemes(“excitation schemes”). During each excitation cycle, the sensor module240 can selectively sense resulting signal(s) from one or more sensingelements of the sensor electrode collection 208. Each excitation cyclehas an associated time period during which sensing signals are drivenand resulting signals measured.

In one type of excitation scheme, the sensor module 240 can selectivelydrive sensing elements of the sensor electrode collection 208 forabsolute capacitive sensing. In absolute capacitive sensing, the sensormodule 240 drives selected sensing element(s) with an absolute sensingsignal and senses resulting signal(s) from the selected sensingelement(s). In such an excitation scheme, measurements of absolutecapacitance between the selected sensing element(s) and input object(s)are determined from the resulting signal(s). In an example, the sensormodule 240 can drive selected sensor electrodes 220, and/or selectedsensor electrodes 230, with an absolute sensing signal. In anotherexample, the sensor module 240 can drive selected sensor electrodes 210with an absolute sensing signal.

In another type of excitation scheme, the sensor module 240 canselectively drive sensing elements of the sensor electrode collection208 for transcapacitive sensing. In transcapacitive sensing, the sensormodule 240 drives selected transmitter sensor electrodes withtransmitter signal(s) and senses resulting signals from selectedreceiver sensor electrodes. In such an excitation scheme, measurementsof transcapacitance between transmitter and receiver electrodes aredetermined from the resulting signals. In an example, the sensor module240 can drive the sensor electrodes 230 with transmitter signal(s) andreceive resulting signals on the sensor electrodes 220. In anotherexample, the sensor module 240 can drive selected sensor electrodes 210with transmitter signal(s), and receive resulting signals from others ofthe sensor electrodes 210.

In any excitation cycle, the sensor module 240 can drive sensingelements of the sensor electrode collection 208 with other signals,including reference signals and guard signals. That is, those sensingelements of the sensor electrode collection 208 that are not driven witha sensing signal, or sensed to receive resulting signals, can be drivenwith a reference signal, a guard signal, or left floating (i.e., notdriven with any signal). A reference signal can be a ground signal(e.g., system ground) or any other constant or substantially constantvoltage signal. A guard signal can be a signal that is similar or thesame in at least one of shape, amplitude, frequency, or phase of atransmitter signal or the absolute capacitive sensing signal.

“System ground” may indicate a common voltage shared by systemcomponents. For example, a capacitive sensing system of a mobile phonecan, at times, be referenced to a system ground provided by the phone'spower source (e.g., a charger or battery). The system ground may not befixed relative to earth or any other reference. For example, a mobilephone on a table usually has a floating system ground. A mobile phonebeing held by a person who is strongly coupled to earth ground throughfree space may be grounded relative to the person, but the person-groundmay be varying relative to earth ground. In many systems, the systemground is connected to, or provided by, the largest area electrode inthe system. The capacitive sensor device 200A or 200B can be locatedproximate to such a system ground electrode (e.g., located above aground plane or backplane).

The determination module 260 performs capacitance measurements based onresulting signals obtained by the sensor module 240. The capacitancemeasurements can include changes in capacitive couplings betweenelements (also referred to as “changes in capacitance”). For example,the determination module 260 can determine baseline measurements ofcapacitive couplings between elements without the presence of inputobject(s). The determination module 260 can then combine the baselinemeasurements of capacitive couplings with measurements of capacitivecouplings in the presence of input object(s) to determine changes incapacitive couplings.

In an example, the determination module 260 can perform a plurality ofcapacitance measurements associated with specific portions of thesensing region 120 as “capacitive pixels” to create a “capacitive image”or “capacitive frame.” A capacitive pixel of a capacitive imagerepresents a location within the sensing region 120 in which acapacitive coupling can be measured using sensing elements of the sensorelectrode collection 208. For example, a capacitive pixel can correspondto a transcapacitive coupling between a sensor electrode 220 and asensor electrode 230 affected by input object(s). In another example, acapacitive pixel can correspond to an absolute capacitance of a sensorelectrode 210. The determination module 260 can determine an array ofcapacitive coupling changes using the resulting signals obtained by thesensor module 240 to produce an x-by-y array of capacitive pixels thatform a capacitive image. The capacitive image can be obtained usingtranscapacitive sensing (e.g., transcapacitive image), or obtained usingabsolute capacitive sensing (e.g., absolute capacitive image). In thismanner, the processing system 110A can capture a capacitive image thatis a snapshot of the response measured in relation to input object(s) inthe sensing region 120. A given capacitive image can include all of thecapacitive pixels in the sensing region, or only a subset of thecapacitive pixels.

In another example, the determination module 260 can perform a pluralityof capacitance measurements associated with a particular axis of thesensing region 120 to create a “capacitive profile” along that axis. Forexample, the determination module 260 can determine an array of absolutecapacitive coupling changes along an axis defined by the sensorelectrodes 220 and/or the sensor electrodes 230 to produce capacitiveprofile(s). The array of capacitive coupling changes can include anumber of points less than or equal to the number of sensor electrodesalong the given axis.

Measurement(s) of capacitance by the processing system 110A, such ascapacitive image(s) or capacitive profile(s), enable the sensing ofcontact, hovering, or other user input with respect to the formedsensing regions by the sensor electrode collection 208. Thedetermination module 260 can utilize the measurements of capacitance todetermine positional information with respect to a user input relativeto the sensing regions formed by the sensor electrode collection 208.The determination module 260 can additionally or alternatively use suchmeasurement(s) to determine input object size and/or input object type.

FIG. 3 is a schematic diagram of a routing configuration 300, accordingto an example. As shown, the routing configuration 300 includes arouting 304 for a sensor electrode 302 (which may, for example, be asensor electrode such as sensor electrodes 220 or sensor electrodes 230of FIG. 2A, or sensor electrodes 210 of FIG. 2B) and a routing 312 for asub-pixel, as well as a sensor electrode 302. Processing system 110 iscoupled to sensor electrode routing 304 and sub-pixel routing 312

The sensor electrode routing 304 electrically couples sensor electrode302 to signal processing unit 306 (which may be a portion of processingsystem 110). The sub-pixel routing 312 electrically couples a displaysub-pixel (not shown) to a source driver (also not shown), which may bea part of processing system 110 of FIG. 1. Coupling impedance 310represents a capacitive coupling between sensor electrode routing 304and sub-pixel routing 312. The coupling impedance 310 exists due to theproximity of these two elements to each other.

In operation, processing system 110 drives sensor electrode 302 forsensing. In response, the sensor electrode 302 provides a signal tosignal processing unit 306, which processes the signal to generateprocessed sensing signal 308, which may be processed by other elementsin processing system 110 to determine presence of an input object 140proximate to sensor electrode 302. Driving sensor electrode 302 maycomprise varying the voltage at the sensor electrode 302 with respect tothe input object 140 so that a current is induced on sensor electroderouting 304 that is dependent on the degree of capacitive couplingbetween the input object 140 (if present and/or capacitively coupled tosensor electrode 302) and sensor electrode 302. The current induced insensor electrode routing 304 in response to driving the sensor electrode302 is labeled as “if” in FIG. 3. Note that driving the voltage atsensor electrode 302 with respect to the input object 140 might be doneby maintaining the sensor electrode 402 at a fixed voltage with respectto system ground. This may be done by providing a modulated power supplythat modulates the power supply and ground voltages of input device 100with respect to an external voltage such as voltage associated with aninput object 140.

The signal processing system 306 processes the current signal receivedon sensor electrode routing 304 to generate a processed sensing signal308 for further processing including determination of presence of aninput object 140. The signal processing system 306 includes variouselements that perform functions such as sampling through chargeintegration, signal filtering, demodulation, and the like, and caninclude elements such as an operational amplifier with capacitivefeedback, a demodulator, a filter, and other mechanisms.

Sub-pixel routing 312, which provides signals for updating displayelements (not shown), may be near to sensor electrode routing 304. Whena signal is driven onto sub-pixel routing 312 by a source driver, somecurrent is driven onto sensor electrode routing 304 due to couplingimpedance 310. This current is referred to as a “corrupting current” ic,and flows to sensor electrode routing 304.

The current that arrives at signal processing unit 306 is thus acombination of the corrupting current “ic” from sub-pixel routing 312and the current from sensor electrode “it”. (Note that corruptingcurrent may come from a most-nearby sub-pixel routing trace, as well asfrom other traces that are nearby). Thus, the processed sensing signal308 is affected by current induced by display updates that is unrelatedto an input object 140 near sensor electrode 302. By affecting what isprocessed by signal processing unit 306, the corrupting current hindersthe ability of processing system 110 to detect presence of an inputobject 140.

To improve ability to detect presence of an input object 140, techniquesfor removing the corrupting current are provided herein. Thesetechniques help with making the processed signal to accurately reflectan input object 140 near sensor electrode 302. In general, thetechniques involve averaging consecutive sensing frames together tocancel out the corruption current, taking advantage of the fact thatdisplays typically perform frame inversion. Frame inversion typicallyinvolves altering the polarity of voltage driven by a source driver withrespect to a middle, “zeroed” voltage, in order to refrain from causinga malfunction of the display elements. Display elements (such as aliquid crystal material) can be fouled by repeated application ofvoltage of the same polarity. The interference remover 320 of processingsystem 110 may perform at least a portion of the techniques for removingthe corrupting current. The interference remover 320 may comprise, forexample, a specifically designed interference remover circuit configuredto perform the functionality described herein, or a programmable circuit(e.g., a microcontroller) programmed to perform the functionalitydescribed herein. Other technically feasible embodiments are possible aswell. The techniques for removing corrupting current are describedbelow.

FIG. 4 is a diagram that illustrates aspects of frame inversion,according to an example. FIG. 4 illustrates a first frame portion 402and a second frame portion 404. Each frame portion is associated with aparticular frame and shows only four sub-pixels of a display, but itshould be understood that frame inversion is generally applied tosubstantially each sub-pixel in a display. The frame for the secondframe portion 404 is immediately subsequent to the frame for the firstportion 402.

For the first frame portion 402, each of the sub-pixels 406 illustratedis driven with a voltage having a first polarity (i.e., above or below amiddle “zero” voltage), indicated with an “X.” For the second frameportion 404, each of the sub-pixels 406 is driven with a voltage havinga second polarity that is opposite from the first polarity, indicatedwith an “O.” In accordance with frame inversion, frames of the displayalternate between states like the first frame 402 and the second frame404. In other words, each frame, a sub-pixel is driven with a voltagethat is opposite in polarity to the voltage with which that sub-pixelwas driven the previous frame.

Note that although sub-pixels change polarity every frame, it is notnecessary for all sub-pixels (or even for neighboring sub-pixels) of anyparticular frame inversion scheme to change from and to the samepolarities. Thus, while four neighboring sub-pixels 406 are illustratedin FIG. 4 as each having the same polarity, it should be understood thatneighboring sub-pixels may have different polarities in any particularframe. Schemes such as line inversion, dot inversion, and other morecomplex schemes are known and are possible. Each such scheme isconsidered to be a “frame inversion” scheme in that polarity for anyparticular sub-pixel is reversed each frame.

FIG. 5 is a graph 500 that illustrates the effect of frame inversion fora particular sub-pixel, according to an example. As can be seen, voltagefor the sub-pixel is at a positive voltage (represented by “+”), thentransitions to a negative voltage (represented by “+”), and then back tothe positive voltage (“+”).

When voltage transitions to a positive voltage for a particularsub-pixel, the sub-pixel routing 312 to that sub-pixel induces a currentflow in sensor electrode routing 304 that is equal to

${C\frac{V}{t}},$

where C is the capacitance of the capacitive coupling (couplingimpedance 310) and V is the voltage difference between the voltage atthe sub-pixel routing 312 and the sensor electrode routing 304. Then,when voltage transitions to a negative voltage for the next frame andthe same sub-pixel, the sub-pixel routing 312 to that sub-pixel inducesa current flow in sensor electrode routing 304 that is equal to

${- C}{\frac{V}{t}.}$

It the brightness value for the sub-pixel is the same or substantiallythe same (i.e., if the display image is not changing quickly), then thevoltage V is the same or substantially the same for the two consecutiveframes. This means that the amount of corrupting current injected bydisplay elements is roughly equal but of opposite polarity onconsecutive frames.

FIG. 6 is a graph 600 illustrating frame averaging for cancellation ofcorrupting current, according to an example. The graph 600 illustratesfour frames, labeled F₁, F₂, F₃, and F₄. These frames are sensing anddisplay update frames in which one “sensing frame” (or capacitive frame)and one “display frame” or “display update frame” occurs.

Referring momentarily to FIG. 3, note that signal processing unit 306may convert current signals received from sensor electrode 302 to adigital signal. The digital signal value is generally dependent on thecurrent signal received at signal processing unit 306 and thus may besaid to have a component associated with it and a component associatedwith ic. Digital components of the processing system 110 may receive thedigital signal and process the digital signal further to determinelocation of an input object 140.

Referring back to FIG. 6, to remove corrupting current from the digitalsignal, processing system 110 (specifically, interference remover 320)averages two sensing frames together. Averaging two sensing framesincludes, for each capacitive pixel, adding output values representativeof the current received, and dividing by two. Because the corruptingcurrent changes sign each frame, the corrupting current from twoconsecutive frames, when summed, adds to 0. Mathematically, the averagevalue for a capacitive pixel for two consecutive frames is:

$\frac{\left( {{it} + {C\frac{V}{t}}} \right) + \left( {{it} - {C\frac{V}{t}}} \right)}{2},$

which equals

$\frac{2\; {it}}{2},$

which equals it, which has no contribution from the display-originatingcorrupting current. For determining presence of an input object 140, theaveraged frame is used in place of the later of the frames that areaveraged together. For example, if an earlier frame F1 is averaged witha later frame F2, the averaged frame is used in place of the later frameF2 for purposes of determining presence of an input object 140.

Note that a first capacitive frame of sensing data has no priorcapacitive sensing frame with which to perform averaging, so, in someembodiments, when sensing begins, there is one frame of lag where nosensing data is output—the first frame is dropped and not used fordetermining presence of an input object (except indirectly throughaveraging with the next frame). In other embodiments, the first frame isnot dropped, and is used to determine presence of an input objectdespite possibly including components from noise.

Note also that sensing and display updating may be performed“simultaneously.” The term “simultaneously” means that touch sensing forone or more sensor electrodes of the input device 100 is performed atthe same time as display updates with one or more of the displayelements of the input device 100. Sensing and display updating mayalternatively be performed at different times, but in a single, commonframe in which display updates and sensing is performed. Sensing anddisplay updating may alternatively be performed in separate but at leastpartially overlapping periods. In other words, display updating may beperformed during a first period and sensing may be performed during asecond period, where the first period and second period at leastpartially overlap.

Sensing electrodes may be integrated with display elements. For example,display elements may include two electrodes that form a capacitor with amaterial between the two electrodes that varies characteristics relatedto light transmitted through that material based on a voltage acrossthat material. One of those electrodes provides a reference voltageagainst which the other electrode may apply a voltage to set thevariable characteristic (e.g., light polarization direction) of thetransmissive material. Setting the variable characteristic of thetransmissive material may be referred to herein as “updating the displayelement.”

Sensing and display updating may involve updating display elements whilealso sensing with sensing elements integrated with those displayelements. Alternatively or additionally, sensing may involve updatingdisplay elements while sensing with sensing elements other than thosethat are integrated with the display elements, as well as sensing withsensing elements while updating display elements other than those thatare integrated with the sensing elements.

FIG. 7 is a flow diagram of a method 700 for removing corruptingcontribution generated by display elements from a sensing signal,according to an example. Although described with respect to the systemof FIGS. 1-3, those of skill in the art will understand that any systemconfigured to perform the steps in various alternative orders is withinthe scope of the present disclosure.

As shown, the method 700 begins at step 702, where processing system 110performs capacitive sensing and performs display updating in a firstframe. Capacitive sensing includes driving electrodes with signal andreceiving signals in return. Display updating includes driving a voltageto a display element and may induce a corrupting current on a sensorelectrode routing that carries the received sensing-related signals. Thesensing-related signals may thus include data indicative of an inputobject 140 near the driven sensor electrode and also includes acorrupting current related to the display signal.

At step 702, processing system 110 performs capacitive sensing anddisplay updating in a second frame. The second frame is performedsimilarly to a first frame but for display updating, frame inversionoccurs. This means that the voltage polarity for each display sub-pixelis the inverse of the voltage polarity for the sub-pixels in the prior(first) frame.

At step 704, processing system 110 averages the two sensing frames tocancel out corrupting current. Averaging two sensing frames involves,for each capacitive pixel, adding the corresponding value for the firstframe to the value for the second frame together and dividing by two.Note that a value approximately equal to this average value could beused as well. Because of the reverse in polarity for the display data,this averaging cancels out the corrupting signal.

Note that in some embodiments, averaging two sensing frames may involvesubtracting pixel values for one frame from corresponding pixel valuesof the other frame and using the average difference, a maximumdifference or a minimum difference or a difference between maximumdifference and minimum difference as an adjustment for the pixel valuesof either frame to remove noise. In some embodiments, averaging twosensing frames may be done as a weighted average, where instead ofsumming pixels and dividing by two, the average skews towards the valuesof one frame or another, depending on a weight value, which may (or maynot) differ between pixel positions. Additionally, in some embodiments,instead of corrected each pixel individually, the correction value forall pixels could be determined based on correction values determined forone or a set of pixels. Note that although some techniques for averagingsensing frames are described herein, other techniques are possible.

The method 700 may be performed continuously, meaning that a first framemay be averaged with a second frame to obtain data for the second frame.Then a second frame may be averaged with a third frame to obtain datafor the third frame, and so on.

Advantageously, techniques are provided whereby corrupting signalswithin a sensing signal is removed. The techniques generally includeaveraging two frames of sensing data together. Because frame inversionis typically performed for display data, the corrupting currentcontributed by display updates varies in polarity from negative topositive and back each frame. Thus, the corrupting current variesbetween positive and negative and back each frame. Averaging consecutivesensing frames together thus cancels out the corrupting currents. Thesetechniques represent simple operations that can be performed digitallyand without addition of components and that serve to remove corruptingsignals from display elements.

Thus, the embodiments and examples set forth herein were presented inorder to best explain the present invention and its particularapplication and to thereby enable those skilled in the art to make anduse the invention. However, those skilled in the art will recognize thatthe foregoing description and examples have been presented for thepurposes of illustration and example only. The description as set forthis not intended to be exhaustive or to limit the invention to theprecise form disclosed.

What is claimed is:
 1. A processing system configured for simultaneouslyupdating a display and performing capacitive sensing, the processingsystem comprising: a source driver configured to drive a source linewith a first source driver voltage during a first time period and toreceive resulting signals on a routing trace coupled to a sensorelectrode during a second time period that at least partially overlapswith the first time period, the routing trace and the source line beingrouted proximate each other; and an interference remover configured toacquire first resulting signals during a first display update period andsecond resulting signals during a second display update period, and toremove display interference from the second resulting signals bycombining the first resulting signals and the second resulting signals,wherein first display signals provided for display updates during thefirst display update period are frame-inverted with respect to seconddisplay signals provided for display updates during the second displayupdate period.
 2. The processing system of claim 1, wherein theinterference remover is configured to combine the first resultingsignals and the second resulting signals by: adding the first resultingsignals to the second resulting signals.
 3. The processing system ofclaim 1, wherein the interference remover is configured to combine thefirst resulting signals and the second resulting signals by: averagingthe first resulting signals with the second resulting signals.
 4. Theprocessing system of claim 3, wherein removing the display interferencefrom the second resulting signals comprises: producing aninterference-filtered set of resulting signals corresponding to thesecond sensing frame.
 5. The processing system of claim 1, wherein: thefirst resulting signals comprise resulting signals for a first sensingframe; and the second resulting signals comprise resulting signals for asecond sensing frame that is consecutive to the first sensing frame. 6.The processing system of claim 5, wherein: the second sensing frame issubsequent to the first sensing frame.
 7. The processing system of claim1, wherein: the source line and the routing trace are disposed in acommon layer.
 8. The processing system of claim 1, wherein: the sourceline and the routing trace are disposed in separate layers; and thesource line is parallel to the routing trace.
 9. The processing systemof claim 1, wherein the interference remover is further configured to:drop an initial sensing frame.
 10. An input device configured forsimultaneously updating a display and performing capacitive sensing, theinput device comprising: a display element coupled to a source line; asensor electrode coupled to a routing trace, the routing trace and thesource line being routed proximate each other; and a processing systemcoupled to the source line and the routing trace, the processing systemcomprising: a source driver configured to drive the source line with afirst source driver voltage during a first time period and to receiveresulting signals on the a routing trace during a second time periodthat at least partially overlaps with the first time period; and aninterference remover configured to acquire first resulting signalsduring a first display update period and second resulting signals duringa second display update period, and to remove display interference fromthe second resulting signals by combining the first resulting signalsand the second resulting signals, wherein first display signals providedfor display updates during the first display update period areframe-inverted with respect to second display signals provided fordisplay updates during the second display update period.
 11. The inputdevice of claim 10, wherein the interference remover is configured tocombine the first resulting signals and the second resulting signals by:adding the first resulting signals to the second resulting signals. 12.The input device of claim 10, wherein the interference remover isconfigured to combine the first resulting signals and the secondresulting signals by: averaging the first resulting signals with thesecond resulting signals.
 13. The input device of claim 12, whereinremoving the display interference from the second resulting signalscomprises: producing an interference-filtered set of resulting signalscorresponding to the second sensing frame.
 14. The input device of claim10, wherein: the first resulting signals comprise resulting signals fora first sensing frame; and the second resulting signals compriseresulting signals for a second sensing frame that is consecutive to thefirst sensing frame.
 15. The input device of claim 14, wherein: thesecond sensing frame is subsequent to the first sensing frame.
 16. Theinput device of claim 10, wherein: the source line and the routing traceare disposed in a common layer.
 17. The input device of claim 10,wherein: the source line and the routing trace are disposed in separatelayers; and the source line is parallel to the routing trace.
 18. Theinput device of claim 10, wherein the interference remover is furtherconfigured to: drop an initial sensing frame.
 19. A method forsimultaneously updating a display and performing capacitive sensing, themethod comprising: driving a source line with a first source drivervoltage during a first time period; receiving resulting signals on arouting trace coupled to a sensor electrode during a second time periodthat at least partially overlaps with the first time period, the routingtrace and the source line being routed proximate each other; acquiringfirst resulting signals during a first display update period and secondresulting signals during a second display update period; removingdisplay interference from the second resulting signals by combining thefirst resulting signals and the second resulting signals, wherein firstdisplay signals provided for display updates during the first displayupdate period are frame-inverted with respect to second display signalsprovided for display updates during the second display update period.20. The method of claim 19, wherein combining the first resultingsignals and the second resulting signals comprises: averaging the firstresulting signals with the second resulting signals.